We want to get right to the fast-moving developments on syria. President obama, addressing the nation last night. Abc's jonathan karl has the latest and joins us this morning from the white house. Good morning, jon. Reporter: Good morning, robin. The president is dispatching secretary of state john kerry to geneva, for a meeting with the russians, hoping for a diplomatic shugolution, as he keeps open the threat of military force. My fellow americans. Reporter: Describing in gruesome detail, the use of chemical weapons. The images from this massacre are sickening. Men, women, children, lined up in rows, killed by poison gas. Others foaming at the mouth, gasping for breath. This is not a world we should accept. Reporter: America is not the world's policeman, he said. But such horrors demand a response. When, with modest effort and risk, we can stop children from being gassed to death, and thereby make our own children safer over the long run, i believe we should act. That's what makes america different. Reporter: The new possibility of a diplomatic breakthrough has put a military strike on hold. But if it comes -- let me make something clear. The united states military doesn't do pinpricks. Even a limited strike will send a message to assad that no other nation can deliver. Reporter: The threat of force is already working, he said, leading the russians to make their offer to broker a deal to get syria to turn over all of its chemical weapons. But, he added -- it's too early to tell whether this offer will succeed. And any agreement must verify that the assad regime keeps its commitments. Reporter: The senate was supposed to have a vote on the syria resolution today. The president asked all congressional voting on this to be delayed. And it's not just about diplomacy, robin. He was going to lose those votes in the house and probably even in the senate. He's asking for that delay. And frankly, the people I've spoken to this morning on the hill, suggested nothing he said last night would change the vote count. As you said, there is a delay right now. Many people want to know, what happens next, jon? Reporter: Well, that's a good question. Right now, some time for diplomacy. There's no timeframe for the vote. Some people in congress doubt there ever will be a vote on this. But for now, it's all focused on the diplomacy. And the white house has not put a firm timeline on how long that can go on. Continues to be a fluid situation. Jonathan karl there at the white house. Thank you.

This transcript has been automatically generated and may not be 100% accurate.

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